Wireless telegraph apparatus



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F. Lowl-:NSTEIN WIRELESS S TELEGRAPH APPARATUS Filed June '28, 1910 13 SheetsLsheet' 13 Patented Feb. 15, 1927.`

UNITED STATES 1,618,017 PATENT OFFICE.

FRITZ LOWENSTEIN, OF NEW YORK, N. Y.; JOHN C. WAIT, ADMINISTRATOR Ol' SAID FRITZ LOWENSTEIN. DECEASED, ASSIGNOR, BY MESNE ASSIGNMENTS, T RADIO CORPORATION OIYAMERICA, A CORPORATION OF DELAWARE.

WIRELESS TELEGBAPH APPARATUS.

Application led June 28, 1910. Serial No. 569,324.

i\'[y invention relates to improvements in wireless telegraphy.

'The objects of my invention are to provide a simple, readily operated apparatus which will enable the operator to quickly adjust and tune his apparatus both in receiving and transmitting. "ith this general object in view my invention consists in the features, details of construction and combination of parts which are first described in connection with the accompanying drawings and then more particularly pointed out in the claims.

Referring toV the drawings:

Fig. 1 is a diagram of transmitter circuits employed by me;

Fig. `2 is a detailed elevation of the mechanical parts for operating the transmitter;

Figs. 3, 4, la and 5 are diagrammatic views of different forms of receiving circuits embodying my invention;

Fig. is a plan view of the receiver shown diagrammatically in Fig. 4;

Figs. 7 and 8. are diagrams illustrating the principles involved in my receiving elements;

F ig. 9 is a diagram illustrating the characteristics of some elements of the apparatus employed in Fig.

Fig. 10 is a plan view and Fig. 11 a Vertical section of the variable self inductance and capacity employedV by me;

Fig. 12 is a diagram illustrating the 4method of determining the constants ot an antenna;

Fig. 13 is a diagram showing the gearing.

Referring to the drawings, and more particularly to Fig. 1, which illustrates ydiagrammatically a practical form of the transmitter circuits, 100 represents a line switch connecting direct current supply mains 101 with circuit 102 of a direct current motor 103 having series and shunt field windings 104 and 105, respectively. Said motor'is arranged to drive alternating current generator 106 whose series and shunt field windings are indicated at 107 and 108, respectively.' A regulator for the generator field is indicated at 108; and a generator-compounding adjuster at 108). Protecting devices 109, 110, 111 and 112 are provided for protecting against high frequency 'high potential break down of the direct current motor, 4alternating current generator, and

the shunt field windings and series field windings of the generator, respectively. These protecting devices may be of any usual or suitable form and require no detailed description.

The alternating current generator supplies power to the primary 113 of a resonance transformer of which the secondary is indicated at 114. this secondary feeding the closed or oscillating circuit of the transmitter system. The secondary may have its end turns air insulated as indicated at 114". A protecting device for the transformer is provided as shown at 115. The oscillating circuit includes condenser 116,v spark ap 117, which is here shown as of the quenc ed type, primary inductance or'helix 118, and loose coupling coil 129.

The spark gap may be cooled as by fan 119, whose circuit isprovided with protecting device 120.

By means of lightning switch 121, the antenna 122 may be connected either to ground, or to conductor 123 which, in turn, may be connected by arm 124 of an antenna switch device, which will be described later in detail, l either to the receiver circuit through lead 125, or to ground throu h lead 126, variable inductance 127, movab e contact 9, secondary inductance 128, double movable bridging contact 12, 13, primary inductance 118, coupling coil 129, and movable contact 8. A hot wire ammeter 130 may-'be inserted in the ground connection, as shown. The variable loose coupling coil 129 between the primary inductance 118 and the secondary inductance 128 is adjustable about its axis 131 that the coil may be moved to bring its axis either in line with the axes of coils 11E;` and 128 or at right angles to said axes; or the coupling coil may be made to assume any intermediate position between these eX- tremes. a

The loose coupling shaft is diagrammatically indicated in Fig. 1, while in Fig. 2 are shown means for turning the shaft, which means will be more fully hereinafter described. The mutual induction or coupling between the primary and secondary helices may therefore be varied as desired.

The primary and secondar helices are tapped oit' at certain points an as indicated in Fig. 1, are connect-edv in groups to corresponding contact points I, II, III, IV and V, and 1, 2,3, 4 and 5. These taps are arranged so that the primary and secondary circuits as shown dia ammaticall'y in Fig. 1 remain in syntony or any positlon of the ltransmitter lever 6, or for any position of the transmitter wheel 7, Fi 2. The two contact brushes 8 and 9 whic are o rated by the wheel 7 are turned jointl y provision of bevel gears 10 and 11 an insulator shaft 7. The contact brush 12 of the' primary helix and 13 of the secondary helix are "one piece mechanically placed in olposite directions on one a and there ore movejointly by the operation of the lever 6. As shownn Fig. 1. the o lever 6 will change the se'f-inductance of the prima anfd secondary circuits in large steps there y enabling the operator to send out in quick succession live different wave' -lengths over a comparatively large ran e.

'lengths are obtained in ready succession which tive wave lengths have smaller steps between themselves than the wave lengths obtained by operation of the lever 6.

An intermittent gear 14-15 is provided by meansof which ,after each complete revolution vof the wheel the lever is advanced to the next contact point. I am thus enabled to obtain 25 diierent wave lengths b the transmitter arrangement as shown in ig. 2

by a continuous turning of the wheel 7 for five complete revolutions.

f The Iobject of this design is to adjust the transmitter rapidly to any wave lengths `de sired without recourse to several operations or diagramsand' to provide means for interference.

In Fig. 1 thesending key is shown, which combines the featureV of a minimum of arcin with safetyfroi'n danger due to high voltage currents Yon the other apparatus when the key is open. In this view 16 represents a seliE-inductance with two windings which are connected in such way that when they are traversed by the primary current their magnetomotive forces are opposite and equal so as not to produce magnetic field in the iron core. When sending key 17 is-depressed during transmitting thisdevice 16 not oier. any more resistance to the passage of the current than that given by the ohmic resistances of the windings. Key 17 has two currentl breaks 18 and `19. In rethekey, contact 18 will break first ration of thel and as the current which flows through this contact can be made to be a' small part only of the total current of the primary circuit, the arcing at this point 18 is greatly reduced. After contact at point 18 has broken the primarycurrent can only run through the upr half of the iron core winding and exertmg its magneomotive force will produce a considerable counterelectromotive force thereby reducing the total primary current to a small fractionof its original value, so that at the moment when contact 19 breaks the current is so small that there is no appreciable arcing at this break. For quick and reliable operation of the transmitter 'non-arcing keys are very important and this therefore constitutes an important feature of my invention.

The novel antenna switch device above referred to is useful particularl in connection with what is known as brea r key operation, .whereby the o rator is enabled to listen in for incoming signals during the brief intervals occurring between the dots and dashes of his own signals. In the present instance, this antenna switch device has a shaft 132 of suitable insulating material such as micanite or the like, to which are secured the metal contacter 124 above mentioned, and another metal contacter 133 which is adapted to close the cap 134 be tween leads 135 and 136 when the switch is in a position to permit this. The leads 135, 136, connect the alternating current generator with the resonance transformer when key 17 is depressed into sending position and gap 134 is closed. The transmitter key 17 has an insulated bridging contact 17 attached to the rear part of its lever, and when the key is in rest position, this contact closes the open gap 137 in circuit 138, 139 which includes the magnet 140 whose iron armature 141' is mounted on the switch shaft 132. A tension spring 142 is arranged to draw the magnet armature away from the magnet' 'when the circuit of the latter is open, thereby moving the switch device to.close the gap 134 and connect the antenna-to lead 126, thus putting the system in. condition for Sending. In the position shown in Fig. 1, however, the transmitter key is in rest position, the magnet is energized, and it therefore attracts, armature 141 against the action ofthe tension spring. Consequently the circuit 135, 136 is opened, and no power is supplied to the transformer. By means of this arrangement,l whenthe antenna switch is set for receiving, the current from the antenna does not pass through the transmitter inductance, but only through the receiver circuit. In this way the setting of the re` ceiveifor any particular wave length is independent of` the setting of the transmitter.

In the present arrangement. provision is also made for preventing arcing over the contact points 1, 2, 3, 4, and while varying wave lengths through manipulation of the transmitter handle 6. As shown in Fig. 1, the transmitter handle is here rovided with 'an arm 143 carrying an insu ated metallic e thereby to open the power circuit supplying the transformer. The arrangement of parts is such that the bridge 144 closes the magnet circuit just before the movable connector 12, 13 breaks connection between the transmitter helices in passing from one pair of contact points-1, 2, 3, 4 and 5 to the next pair. As soon as connection between the next air of contact points is established, the bridge 144 opens the magnet circuit, whereby the power circuit to the transformer is again closed.

Having now explained the application of certain principles of the invention to a transmitter system, I will proceed to describe a `practical arrangement of the receiver. The

" principal object of my invention, as conc'erns the receiver, is to adjust the primary and secondary circuits thereof in such way that they may automatically remain in tune over a wide range of wave lengths. It has heretofore been considered impossible to 'achieve this result because of the generally adopted views of many experimentcrs and investigators that the behaviour of an antenna is not similar to that of a self-inductance or a capacity. The complex nature ofk the rcactance curves which have been plotted for many antennae has made it appear that an antenna could not be represented in its electrical functions. by simple electrical instrument values or elements like capacity and self-inductance. On the contrary, Ihave found that an antenna may in fact be represented by a lumped capacity and selfinductance.

antenna be plotted in referencetow, (which represents 21rf) as abscissae, a parabola will result. Assuming that a number of reactances at an equal number of frequencies have been measured, then by selecting any two points the parabola may be plotted and from it may be derived the absolute value of the antenna capacity and the absolute value of the antenna self-inductance, which absolute values remain constant for all wave lengths from the natural wave length up. i

If, for example, a' number of values, of

reactances at different frequencies, say five, have been obtalned by actual measurement .of an antenna, these may be plotted as ordinates, with the corresponding wavelengths as abscxssae, thus giving a Graph which 1s a parabola, as illustrated in 4ig. 12. If now any two points iny this parabola be selected and the corresponding ordinates and abscissae measured and their values determined from the scale of the drawing, the constant value C.L of the antenna capacity and the similar value Ln of its self inductance may be `calculated-from the formula:

The frequency may be designated by thev letter f. The quantity Qnff is commonly designated by the letter fw. The reactance of a capacity C is The reactance of a selfinductance L is wL. A circuit containing both capacity and self-inductance has a reactance El@ wL.

lf an antenna be made a part of an oscillatory circuit to which a frequency f1, arbitrarily chosen, be imparted, the antenna may be substituted with impunity by a capacity the reactance` of which, w-C-r is equal to the antenna reactance,

where C., and L.,L are fixed values of capacity and self-inductance, respectively, representing the antenna. Therefore 1 1 10101 w10. This substitution capacity C1L is found by the usual resonance method, viz: WVith the antenna included in an oscillatory circuit a frequency f, is applied (21"f1 wi) llO . LU o 1 and the circuit tuned to resonance; then the antenna is vdisconnected and in its place a condenser is inserted which is then adjusted so as to again obtain resonance. The capacity value C, of this condenser then 1ndicates the reactance value of the antenna:

which formula was to be deduced. A second frequency furnishes a similar equation In these two equations, w1 and lw2 are given (arbitrarily chosen) and C1 and C2 are determined by substitution measurement as above explained; leaving the two unknown quantities Ca and Lal which are found in the usual elementary way of solving two equations for two unknowns. Plotting the values C1 C2 Cn against their corresponding values of 'w2 fwn as abscissae, a paral clearly indicated by the parabolic nature of the above equation written in a general form bola is found as the locus of the values as l Ca where A. stands :for the constant y B for the Variable fw.

. The values thus found are to be made elements for artificial antenna to be used in the local circuit.

Thereby I am enabled to imitate the seemingly variable antenna by two constant values of a Ycondenser and a self-inductance. Fig. 3 shows such an artificial antenna in Ls and Cs. This artificial antenna, that is to say, the lumped self-inductance and capacity equivalent to that of the actual antenna, is provided in the local circuit to make this circuit in effect identical with the actual antenna circuit. Thereby I am enabled to move the four variable elements of the receiver L Cf, L and C simultaneously by the employment of gears or other mechanical means without at any moment disturbing syntony between the two circuits. The artificial antenna may be made a copy of the antenna to which the apparatus is to be attached, all as actually shown in Fig. 3. The artificial antenna of the local circuit may be predetermined and the real antenna adjusted by a standardizing self-inductance and capacity so as to make itsy values equal to that of the predetermined artificial antenna.

Fig. 3 shows a ,standardizing self-inductance L', which serves to convert the primary circuitto the predetermined standard value. A standardizing condenser should be provided for the same reason. It has been omitted in Fig. 3, assumption being made that the antenna itself' was adjusted to the predetermined value. Such a standardized condenser is shown in Fig. 5 at CB. vAs shown in Fig. 3, the detector coupling is variable by plugging the detector circuit around either the variable capacity alone, or the standard artificial capacity alone,Y or around both in series.

In Fig. 4, L (I, II, III, IV) designate the self-nductance of the local receiver which self-inductance is tapped off and connected to a number of contact points 22, a contact arm being provided to cut in or cut out self-inductance. 24 is a variable condenser which is also operated by an angular movement. The characteristics of both the self-inductance and the capacity are shown in Figs. 7 and 8 to be of logarithmic nature. In this case the self-inductance and capacity of the artificial or equivalent standard antenna in the local circuit areembodied in the variable apparatus.

In Fig. T the angles of displacement of the self-inductance and the capacity are shown as abscissae while the ordinates designate the electrical values of the corresponding displacement. The equation for this logarithmic characteristic is given as b We This characteristic also fulfils the condition that the product of any two ordinates is equal to the square of that ordinate which lie-s half way between them. If therefore the self-inductance and the capacity be placed at certain points for the purpose of receiving a signal and then the self-induciance be increased by a certain displacement and the capacity decreased by an equal displacement, the tune of the receiving circuit is thereby not changed, since the tune depends on the product of capacity multiplied by self-inductance. Though therefore no change has been made in the tune of the circuit the stiffness has been changed and it is for this purpose and for the purpose of variable detector coupling that this logarithmic characteristic has been chosen.

" Fig. 8 shows diagrammatically how a .over the contact points 22.

sub-division. -Both scales are indicated by 27 in Figs. 6, 7, 8, 10 and 11. Theprimary .c"oil of 'a loose coupling is indicated by 28 in Figs. 4, 5, and 6. In Fig. 4 the loose coupling is indicated at M M. The self-inductance is sub-divided into four. sections I, II, III, IV, Figs. 4 and 6. For the purpose of avoiding losses due to dead coil ends, these sections are connected by section swtiches S S which are operated automatically by the self-inductance arm 23. As is clearly shown in Figs. l() and 11, the selfinductance arm 23 is arranged to be moved so as to make contact successively with the `contact points 22 which are electrically connected by means of studs 22 and suitable leads with the tapping-oft' points of the self-inductance, this latter not being shown in Figs. 10 and 11. Each of the section switches S S is pivoted as at P and is provided with a bifurcated projecting portion Q so disposed that one or the other of its arms always lies in the circular' path in which travels actuating stud 23a which is carried by self-inductance arm 23. As the arm 23 is moved in counter-clockwise direction as indicated by the arrow in Fig. 10, the self-inductance is increased as the armpasses Furthermore the stud 23 acts on the section switches successively to bridge the Gap between section contacts P P, thus cutting inthe sections I, II, III and IV as required. In Fig. 10 the switch at the left is shownv as just being thrown to connect sections I and II. In the same manner as the arm continues to move counter-clockwise the other two section switches will be operated to bring sections III and IV into the circuit. In traveling in the reverse direction, that is, clockwise, the'stud 23a turns the section switches in the opposite direction, opening the gaps between the pairs of contacts P P to cut out the sections successively. The detector circuit is connected by a double throw switch 29, Fig. 4 by which the same may be connected with the antenna circuit to tune the primary. In throwing the switch over, the detector circuit is connected to the local circuit. By suitably maniplulat-ing switches a .(Figs. 3, 4, 4 and 5), t e antenna may be optionally connected to va duplicate or reserve receiver system. Thisarrangement is important in that it ensures uninterrupted .service in case it becomes necessary or desirable to temporarily discontinue the use ofone of the receivers for purposes of repair, etc. In the samel figures is indicated the antenna transfer switch b whereby the antenna may be connected either to-one of the receivers or to the transmitter, as at c. After tuning the local circuit by arbitrarily varyinor the capacity and self-induct-ance an audibility may be obtained which is not a maximum obtainable. For the urpose of obtaining such maximum audibihty the self-inductance and ca acity of the local circuit,I, II, III, IV an 24 are mechanically coupled and turned in such way that one decreases while -the other one increases for the same amount of displacement. By such turning the tune ofthe circuit is not disturbed but the detector coupling alone varied. It is known that there is an optimum of the detector couplin to insure a maximum of audibility.

-Hereto ore it was very tedious to change the stiffness of a circuit and then readjust it to tune, and thus possibly so much time elapsed between two readings that comparisons were impossible. By the introduction of the logarithmic characteristic of self-induction and ca acity I am enabled to vary quickly the sti ness and therewith the detector'coupling without throwing the circuit out of tune. In general, therefore, the percentage increase of self-inductance, capacity and wave length for a given increase of displace- Vme'nt is constant over the whole range. The

apparent sharpness of the tuning is constant and equal to the sharpness of the received 4 wave, no matter which part of the scale is being used- The importance of thus making equal movements of a tuning element )roduce equal percentage changes in sel -inductance, capacity and wave length, will be clear from the following considerations: If, after a receiverI circuit has been tuned, a tuning element thereof, such as the capacity, be changed a certain ercentage, the signals for which the circuit llas been tuned will be practically obliterated. YIn order to effectthis percentage change, a certain geometric movement of the movable part of the tuning element has to be performed. In instruments of the type heretofore known, the geometric movement or displacement is relatively small when the original settin in tune happens to be at the lower end o the instrument scale; while, on the other hand, the actual geometric movement required to get the same percentage change in the value of the tuning element is relatively great if the initial settingv in tune is at the higher end of the scale. For example, in apparatus heretofore used, if a 10 per cent change in capacity were necessary to change from maximum audibility to obliteration, then in the iirst case, assumin the receiver circuit to be in tune at a con enser scale setting of 20, a movement of only 2 over the condenser scale would produce this extreme of the eration; while if the receiver circuit was in tune at a condenser scale setting of150, a movement of 15 would be necessary to roduce the same change. To the eye an to the hand, the receiver would appear to be more sensitive for exact tuning at the lower positions of the condenser than at the higher, since the signals change over their full range of strength in the one case by a movement of 2 only, andin the other case lby a movement of 15. Such differences in the apparent sensitiveness or sharpness of tuning in the receiving apparatus of the heretofore known are due primarily. to the fact that wave lengths, and hence oscillation periods, are proportional to thesquare root product of capacity by inductance, and hence a change in either tuning element affects the tuning in a percentual degrec. Consequently, while equal geometric movements of the tuning mechanism in apparatus heretofore known did not produce egual percentage changes in tuning over dlferent localities on the instrument scale, the arrangement which I have herein disclosed obviates this diiiiculty as hereinbefore explained. It is evident that, in the preferred embodiment of apparatus herein disclosed, the electrical -value of each tuning element is variable in accordance with an exponential function of the distance traversed by the means'movable to vary such value. l

A practical method of mechanically connecting the self-inductance and capacity for operation in conformity with the present invention is shown by way of example in Figs. 10 and 11. The condenser 30, Fig. 1l, shows the movable plates cut ofi at such different angles as to produce the logarithmic characteristic. This movable part of the condenser is turned by means ot a crank 31, a crank disk 32, a shaft 33 and a knob 34. Attached to the shaft 33 is an upper clutch disk 35. The self-inductance arml 23, carrying brush 23 and pointer 26, is attached to a lower clutch disk 36 which turns individually around apost 37 by means of a handle 38. Spring 35 surrounding the vertically movable shaft 33 is compressed between the upper end of post 37 and the upper clutch disk 35, thereby tending to maintain the clutch members out of mutual engagement. Handle 38 is here shown as pivoted at 38', whereby it may be turned down to press brush 23 into firm' contact with any of the contact points 22. Both the condenser and the selfinductance can be varied therefore independently for the purpose of tuning. Once tuning has been established the rubber knob 34 is depressed, thereby engaging clutch 35-36, and turning of the knob will then cause an equal amount of displacement of the self-inductance and .of the capacity-MASV shown in Fig. 10 the capacity increases with type Th1 Ier 40, which rests loosely on the' hub 40 of shown, spring 39 1s prevented from depress- I 42 secured to a sleeve-42 V4a and 5 the self-inductances and capacities a clock-wise movement whereas the self-inductance increases by a movement in the opposite sense. Therefore the turning of knob 34, .if clutch 35-36 is engaged, will increase the capacity and decrease the selfinductance or vice versa for the same amount of dis lacement, thereby obtaining the end desire To obviate the necessity of holding the knob 34 depressed during the turning of the coupled elements a compression spring 39 has been provided, Fig. 11, which will keep the clutch members in engagement. 's spring is conned between the lower end of stationary post or sleeve 37 -and washcrank disk 32 which disk 'is secured to the vertically slidable shaft 33. The spring .therefore tends to force shaft 33 down so as 'couple the inductance and capacity elements.

Sprlng 39 is of sutiicient strength to overcome the opposing spring 35 before described. In the position of the parts here lng the upper clutch member b means of latch members 41 mounted oneaf spr which press t e latch members inwardl so that their shoulders 41 may engage tlle under side of the washer 40. By pushing down on knob 34, the sloping cam vsurfaces 43A of the disk hub throw the'latches 41 outwardly, thereby releasing washer 40 and the spring 39 confined thereb the clutch 3 5, 36 being thereafter held 1n engagement by said spring. When the knob is moved u ward the washer is lifted until it is caught the projection on the latches and thereby t e clutch lsheld in its disengaged condition.

Figs. 4a and 5 show combinations of the two improvements shown in Fi 3 and 4. .The totalcapacities and self-in uctances of both circuits are of a logarithmic nature, but'in the arrangement illustrated in Fig. 4, due to 1 the natural antenna in the primary circuit and the artificial antennaf, L" and C"., in the secondary circuit, the 'characteristic of the variable apparatus is not truly l'oga'- rithmic but of a character of such naturev l that in conjunction with the constants of the circuits a capacity and self-inductance will result which is of a true logarithmic nature. In lthe arrangement shown in Fig. 5,v 'the values L and C, controlled by the a paratus, include the values Ll and o Fig. 4, and hence the characteristic of said variable apparatus. is truly logarithmic, as in the arrangementv of Fig. 4.

Fig. 9 shows the characteristic of tlliese variables.

In Figs.

of both circuits are' interconnected chanical means like gears, as indicated diavariable rocedure to arrive at the grammatically in Fig. 13, provision also 13 being made for disengaging any one element from the chain of gears for the purpose of individual adjustment. Mechanism for effecting thismay be of an;v suitable character as, for example, adjustable gearing adaptnected h v the gearing aforesaid, the capacities in the two circuits may be varied simultaneously' to vary the wave length while maintaining the circuits in tune, that is to Say, in resonance. By depressing knob 34 of each instrument, the inductan'ces, as well as the capacities, of the two circuits are also mechanically coupled, in which condition it is evident that movement of one of the knobs 34, handles 38, or equivalent controlling members, will produce simultaneous movement of all the tuning elements thus coupled. .T his varies the stiffness in both circuits simultaneously without changing the ratio ot' stiff-,

ness between said circuits and without disturbing syntony. By manipulating the intermediate gearing so as to uncouple the t'wo instruments or sets of tuning elements, either instrument can be individually adjusted to vary the stiffness of the corresponding circuit.' B v releasing knobs 34 further individual adjustment as to wave length can be made. The arrangement above described has, in addition to the combined advantages of the improvements shown in Figs. 3 and 4, an additional combination advantage as follows:

ln actual practice, the respective degrees of stiti'nesses ot' the .primary and secondary circuits may be set to be;t advantage and yet be different from one another. If, under these conditions the two instruments be mechanically coupled, the turning of any one ot' the knobs will change both circuits in such Way that they will remain in syntony andprezerve constant the ratio between the stiffness of the primary circuit and the stiffness ot the secondary circuit The foregoing considerations will posibly be better underiiood. from the following explanation ot' Figs. 7, 8, and 9. Figs. 7 and 8 show a schematic diagram of the characteristics of the timing eem-ents, capacity and self-inductance, and their interaction. On the left-hand side ot Fig. 7 a capacity characteristic is shown, having an initial valuel of a and a final value of I), over` a horizontal scale deflection ot w, where w may vary be tween zero and a maximum value c. The

The difference `of intermediate values of the capacity are chosen so as to follow the law arithms mentioned in this description.,

The above iormula may be Written a: x E2 El lfor two values of y1 and y2 is equal to long as their ratio y- .is constant.

l. This explains the equation yzzkylg/z'given at the right-hand side of Fi 7, where the inductance characteristic is s own as ofthe same nature as the capacity characteristic.

As stated above, the characteristic of the instrument lwas chosen in accordance with a mathematical function which mane.a the ratiothe logarithm of jmoving element 27 of Fig. 7 which is read.

in reference to the fixed pointer shown thereunder.

There remains to be explained how lthe second scale, the'wave length scale, (shown on the upper edge of element 27, Fig. 7) is correct for any setting ot' the capacity and ielf-inductance. The Wave length of an electric voscillation is proportional to the 

